Linear compressor

ABSTRACT

A linear compressor includes a fixed member provided with a compression space, a movable member which linearly reciprocates inside the fixed member to compress refrigerant, one or more springs installed to elastically support the movable member in a motion direction, a first stator applied with a current to produce a magnetic field, a second stator spaced apart from the first stator at a certain interval, a conductor member electromagnetically induced by the magnetic field produced by the first stator and the second stator to make the movable member linearly reciprocate, and a control unit which controls supply of the current with respect to the first stator.

This application is a 35 U.S.C. §371 National Stage entry ofInternational Application No. PCT/KR2008/004347, filed on Aug. 4, 2009,which claims the benefit of the earlier filing date and right ofpriority to Korean Application No. 10-2008-0077168, filed Aug. 6, 2008,the content of which are hereby incorporated by reference herein intheir entirety.

TECHNICAL FIELD

The present invention relates to a linear compressor, and moreparticularly to, a linear compressor which employs a conductor member ina linear motor instead of a magnet to produce a driving force bymagnetic induction and automatically or naturally modulate a coolingcapacity according to a load.

BACKGROUND ART

In general, a compressor is a mechanical apparatus receiving power froma power generation apparatus such as an electric motor, a turbine or thelike, and compressing the air, refrigerant or various operation gases toraise a pressure. The compressor has been widely used for electric homeappliances such as refrigerators and air conditioners, and applicationthereof has been expanded to the whole industry.

The compressors are roughly classified into a reciprocating compressor,wherein a compression space to/from which an operation gas is sucked anddischarged is defined between a piston and a cylinder, and the pistonlinearly reciprocates in the cylinder to compress refrigerant, a rotarycompressor, wherein a compression space to/from which an operation gasis sucked and discharged is defined between an eccentrically-rotatingroller and a cylinder, and the roller eccentrically rotates along aninside wall of the cylinder to compress refrigerant, and a scrollcompressor, wherein a compression space to/from which an operation gasis sucked and discharged is defined between an orbiting scroll and afixed scroll, and the orbiting scroll rotates along the fixed scroll tocompress refrigerant.

Recently, among the reciprocating compressors, a linear compressor hasbeen actively developed because it improves compression efficiency andprovides simple construction by removing a mechanical loss caused bymotion conversion by directly connecting a piston to alinearly-reciprocating driving motor.

FIG. 1 is a side view illustrating a conventional linear compressor. Theconventional linear compressor is installed such that a structurecomposed of a frame 2, a cylinder 3, a piston 4, a suction valve 6, adischarge valve 7, a linear motor 10, a motor cover 18, a supporter 19,a rear cover 20, main springs S1 and S2 and a suction muffler assembly21 is elastically supported inside a shell 1.

The cylinder 3 is fixedly fitted into the frame 2, the discharge valve 7is installed to block one end of the cylinder 3, the piston 4 isinserted into the cylinder 3, and the thin suction valve 6 is installedto open and close a suction hole 5 of the piston 4.

The linear motor 10 is installed such that a gap is maintained betweenan inner stator 12 and an outer stator 14 and a magnet frame 16 canlinearly reciprocate therein. The magnet frame 16 is connected to thepiston 4 by a piston fixing portion 16 c, and linearly reciprocates dueto a mutual electromagnetic force between the inner stator 12 and theouter stator 14 and the magnet frame 16 to operate the piston 4.

The motor cover 18 supports the outer stator 14 in an axial directionand is bolt-fixed to the frame 2 so as to fix the outer stator 14, andthe rear cover 20 is coupled to the motor cover 18. The supporter 19connected to the other end of the piston 4 is installed between themotor cover 18 and the rear cover 20 to be elastically supported by themain springs S1 and S2 in an axial direction, and the suction mufflerassembly 21 which allows suction of refrigerant is also fastened withthe supporter 19.

Here, the main springs S1 and S2 include four front springs S1 and fourrear springs S2 in up-down and left-right symmetric positions around thesupporter 19. When the linear motor 10 operates, the front springs S1and the rear springs S2 move in opposite directions to buffer the shockof the piston 4 and the supporter 19. Moreover, refrigerant existing onthe side of a compression space P serves as a kind of gas spring tobuffer the shock of the piston 4 and the supporter 19.

Accordingly, when the linear motor 10 operates, the piston 4 and thesuction muffler assembly 21 connected thereto linearly reciprocate, andthe operations of the suction valve 6 and the discharge valve 7 areautomatically controlled with variations of a pressure of thecompression space P, so that the refrigerant is sucked into thecompression space P via a suction tube (not shown), the suction mufflerassembly 21 and the suction hole 5 of the piston 4, compressed therein,and discharged to the outside through a discharge cap 8, a loop pipe 9and a discharge tube (not shown) on the shell side.

The linear motor 10 of the linear compressor includes the inner stator12, the outer stator 14, and the magnet frame 16 around the frame 2 asshown in FIG. 1. The inner stator 12 is constructed such thatlaminations are stacked in a circumferential direction, and the outerstator 14 is constructed such that core blocks 14 b are installed on acoil winding body 14 a at certain intervals in a circumferentialdirection.

FIG. 2 is a perspective view illustrating a conventional magnet frame.The magnet frame 16 includes a cylindrical frame main body 16 apositioned between the inner stator 12 and the outer stator 14 of thelinear motor 10, magnets 16 b fixed to some outer portions of the framemain body 16 a, and a piston fixing portion 16 c extended to the insideso that the piston 4 can be fixed to one end of the frame main body 16a. Holes 16 d are formed on one side of the magnets 16 b.

Here, the magnets 16 b are formed on the frame main body 16 a at certainintervals in a circumferential direction. Preferably, eight magnets 16 bare coupled to the outside of the frame main body 16 a at regularintervals.

In the conventional linear compressor, the magnet linearly reciprocatesbetween the inner stator and the outer stator due to a mutualelectromagnetic force. However, it is difficult to employ a cylindricalmagnet because of a high price of the magnet. Even if several bar-shapedmagnets are fixed to form a magnet frame, the unit costs and overallcosts of production still increase.

Moreover, in the conventional linear compressor, the linear motor variesa stroke to modulate a cooling capacity according to a load. To thisend, a complicated control unit is provided, which is accompanied withdesign limitations on sizes of peripheral components. Further, acomplicated control method is required, which increases the costs ofproduction and complicates a manufacturing process. Furthermore, muchpower is consumed for controlling, which degrades efficiency of thewhole compressor.

DISCLOSURE Technical Problem

The present invention is conceived to solve the foregoing problems inthe prior art, and an object of the present invention is to provide alinear compressor wherein a conductor member is used instead of a magnetto simplify the shape and controlling of a linear motor.

Another object of the present invention is to provide a linearcompressor wherein a linear motor is not affected by variations ofexternally-applied power, the linear compressor automatically modulatinga cooling capacity according to a load without adopting a specialcontrol method.

A further object of the present invention is to provide a linearcompressor wherein the construction of a linear motor supplying adriving force to the linear compressor is simplified to improveproductivity.

Technical Solution

According to an aspect of the present invention, there is provided alinear compressor, including: a fixed member provided with a compressionspace; a movable member which linearly reciprocates inside the fixedmember to compress refrigerant; one or more springs installed toelastically support the movable member in a motion direction; a firststator applied with a current to produce a magnetic field; a secondstator spaced apart from the first stator at a certain interval; aconductor member electromagnetically induced by the magnetic fieldproduced by the first stator and the second stator to make the movablemember linearly reciprocate; and a control unit which controls supply ofthe current with respect to the first stator.

In addition, preferably, the linear compressor further includes aconnection member which connects the movable member to the conductormember, wherein the conductor member is a conductor mounted on one endof the connection member.

Moreover, preferably, the linear compressor further includes aconnection member which connects the movable member to the conductormember, wherein the conductor member is formed by alternately stackingan annular iron piece and conductor, and mounted on one end of theconnection member.

Further, preferably, the linear compressor further includes a connectionmember which connects the movable member to the conductor member,wherein the conductor member is a conductor line wound around one end ofthe connection member.

Furthermore, preferably, the first stator includes a coil winding bodywound with a coil, and a core mounted on the coil winding body, and thecontrol unit controls On and Off of current supply with respect to thecoil winding body so as to produce a one-way magnetic field in theconductor member.

Still furthermore, preferably, the springs include one or more of afirst spring installed to elastically support the movable member in arefrigerant compression direction, and a second spring installed toelastically support the movable member in the opposite direction to therefrigerant compression direction.

Still furthermore, preferably, at least some portion of the conductormember is positioned between the first stator and the second stator.

Still furthermore, preferably, the first stator includes first andsecond coil winding bodies spaced apart at an interval in an axialdirection and wound with a coil, respectively, and a core mounted on thefirst and second coil winding bodies, and the control unit performs acontrol to supply currents having a phase difference to the first andsecond coil winding bodies to produce a two-way magnetic field in theconductor member.

Still furthermore, preferably, the coil is wound around the first andsecond coil winding bodies in the same direction, and a capacitor isconnected in series to one of the first and second coil winding bodies.

Still furthermore, preferably, the control unit supplies currents havinga phase difference of 90° to the first and second coil winding bodies.

Still furthermore, preferably, the springs are a first spring installedto elastically support the movable member in a refrigerant compressiondirection, and a second spring installed to elastically support themovable member in the opposite direction to the refrigerant compressiondirection.

Still furthermore, preferably, when the movable member operates over acertain speed, a speed of the movable member and a force moving themovable member are inversely proportional at different ratios accordingto an amplitude of a load.

Still furthermore, preferably, when the load increases, the speed of themovable member increases, and the force moving the movable memberincreases.

Still furthermore, preferably, the control unit controls supply of thecurrent to automatically vary a stroke according to the load.

Still furthermore, preferably, when the load increases, an electricalresonance frequency becomes approximate to a mechanical resonancefrequency.

According to another aspect of the present invention, there is provideda linear compressor, including: a fixed member provided with acompression space; a movable member which is provided with a conductormember, and linearly reciprocates inside the fixed member to compressrefrigerant; a plurality of springs installed to elastically support themovable member in a motion direction; a first stator applied with acurrent to magnetically induce the conductor member; a second statorpositioned corresponding to the first stator so that at least someportion of the conductor member can be positioned in a space between thefirst stator and the second stator; and a control unit which controlssupply and interception of power with respect to the first stator,wherein, when a load increases, an electrical resonance frequencybecomes approximate to a mechanical resonance frequency, so that thelinear compressor performs a natural cooling capacity modulationcontrol.

Advantageous Effects

According to the present invention, since the linear motor employs theconductor member instead of the magnet to supply a driving force bymagnetic induction, the mechanism and controlling thereof aresimplified, so that the costs of production are cut down. Moreover,since the linear motor can be driven by minimum elements without aspecial driving unit for controlling, it is possible to improve entireefficiency.

In addition, according to the present invention, the linear motor is notaffected by variations of externally-applied power, and varies a stroketo automatically modulate a cooling capacity according to a load withoutadopting a special control method. It is thus possible to maximizecooling efficiency.

Moreover, according to the present invention, the construction of thelinear motor supplying a driving force to the linear compressor issimplified to improve productivity.

DESCRIPTION OF DRAWINGS

FIG. 1 is a side view illustrating a conventional linear compressor;

FIG. 2 is a perspective view illustrating a conventional magnet frame;

FIG. 3 is a side-sectional view illustrating a first embodiment of alinear compressor according to the present invention;

FIG. 4 is a side-sectional view illustrating a second embodiment of thelinear compressor according to the present invention;

FIG. 5 is a side-sectional view illustrating a third embodiment of thelinear compressor according to the present invention;

FIG. 6 is a perspective view illustrating a first embodiment of aconductor member applied to the linear compressor according to thepresent invention;

FIG. 7 is a perspective view illustrating a second embodiment of theconductor member applied to the linear compressor according to thepresent invention;

FIG. 8 is a perspective view illustrating a third embodiment of theconductor member applied to the linear compressor according to thepresent invention;

FIG. 9 is a graph showing magnetic flux waveforms of a linear motorshown in FIG. 5 by an applied current;

FIG. 10 is a schematic circuit view for applying a current to the linearmotor shown in FIG. 5;

FIG. 11 is a graph showing linear reciprocation magnetic flux operationsof the linear motor shown in FIG. 5; and

FIG. 12 is a graph showing the relation between a slip and a torque ofthe linear motor shown in FIG. 5.

MODE FOR INVENTION

Hereinafter, the present invention will be described in detail withreference to embodiments and drawings.

FIGS. 3 to 5 are side-sectional views illustrating various embodimentsof a linear compressor according to the present invention.

As illustrated in FIGS. 3 to 5, the linear compressor according to thepresent invention is constructed such that a fixed member 120 providedwith a compression space P of refrigerant, a movable member 130compressing refrigerant in the fixed member 120, and a linear motor 200driving the movable member 130 are installed in a hermetic container100. The linear motor 200 includes first and second stators 220 and 240,and a conductor member 260 positioned in a space between the first andsecond stators 220 and 240.

The second stator 240 is fixed to an outer circumference of the fixedmember 120, and the first stator 220 is fixed in an axial direction by aframe 110 and a motor cover 300. Since the frame 110 and the motor cover300 are fastened and coupled to each other by a fastening member such asa bolt, the first stator 220 is fixed between the frame 110 and themotor cover 300. The frame 110 may be formed integrally with the fixedmember 120, or manufactured individually from the fixed member 120 andcoupled to the fixed member 120. A supporter 310 is connected to therear of the movable member 130, and a rear cover 320 is coupled to therear of the motor cover 300. The supporter 310 is positioned between themotor cover 300 and the rear cover 320. Springs S1 and S2 are installedin an axial direction to buffer the shock of the linear reciprocation ofthe movable member 130 with both ends supported by the supporter 310 andthe motor cover 300 or the supporter 310 and the rear cover 320. Here,detailed installation positions and elastic moduli of the springs S1 andS2 may be changed according to the construction and operation of thelinear motor 200, which will be described below in detail.

In addition, a suction muffler 330 is provided at the rear of themovable member 130. The refrigerant is introduced into the movablemember 130 through the suction muffler 330, thereby reducing refrigerantsuction noise.

Some portion of a front end of the movable member 130 has a hollow sothat the refrigerant introduced through the suction muffler 330 can beintroduced into and compressed in the compression space P definedbetween the fixed member 120 and the movable member 130. A suction valve(not shown) is installed at the front end of the movable member 130. Thesuction valve (not shown) opens the front end of the movable member 130so that the refrigerant can flow from the movable member 130 to thecompression space P, and closes the front end of the movable member 130so that the refrigerant cannot flow back from the compression space P tothe movable member 130.

When the refrigerant is compressed over a defined pressure in thecompression space P by the movable member 130, a discharge valve 160positioned at a front end of the fixed member 120 is open. Thehigh-pressure compressed refrigerant is discharged to a discharge cap170, discharged again to the outside of the linear compressor through aloop pipe 180, and circulated in a freezing cycle.

The linear motor 200 includes the first stator 220 through which acurrent flows, the second stator 240 maintaining a gap from the firststator 220, and the conductor member 260 installed maintaining a gapbetween the first and second stators 220 and 240, and magneticallyinduced by the first stator 220 to make the movable member 130 linearlyreciprocate. The linear motor 200 includes a control unit (not shown)which controls supply of a current with respect to the first stator 220.Here, the first stator 220 is an outer stator relatively distant fromthe fixed member 120, and the second stator 240 is an inner statormounted on the fixed member 120.

The linear motor 200 of the linear compressor so constructed is a linearmotor 200 provided with two stators 220 and 240, but a general linearmotor 200 provided with only one current-flowing stator 220 also belongsto the scope of the present invention. In addition, the linearcompressor may include a power unit (not shown) which can receive powerfrom the outside. As the power unit is an element obvious to a person ofordinary skill in the art, explanations thereof are omitted.

As illustrated in FIG. 3, an embodiment of the first stator 220 isconstructed such that core blocks 222 are mounted on one coil windingbody 221 wound with a coil in a circumferential direction. The controlunit controls On/Off of current supply with respect to the coil windingbody 221 so as to produce a one-way magnetic field in the conductormember 260, and produces a force so that the conductor member 260 canmove in a refrigerant compression direction, i.e., a top dead centerdirection. Here, preferably, only the front main springs S1 areinstalled between the motor cover 300 and the supporter 310 to grant arestoration force against a force applied to the movable member 130 bythe linear motor 200. In addition, preferably, the elastic modulus andnumber of the front main springs S1 are determined to be proportional tothe coil winding number of the coil winding body 221. Accordingly, whenthe current is input to the coil winding body 221, a magnet flux forms aclosed circuit along the first and second stators 220 and 240 due to thecurrent flowing through the coil winding body 221. Since an inductionfield is produced in the conductor member 260 due to the magnetic flux,the force is applied in a top dead center direction, so that theconductor member 260 and the movable member 130 move in the top deadcenter direction to compress the refrigerant. Next, when the current isnot input to the coil winding body 221, the magnet flux and theinduction field are vanished, and the conductor member 260 and themovable member 130 move in a bottom dead center direction due to therestoration force of the front main springs S1. Such a process isrepeated to suck, compress and discharge the refrigerant.

As illustrated in FIG. 4, another embodiment of the first stator 220 isconstructed such that core blocks 222 are mounted on one coil windingbody 221 wound with a coil in a circumferential direction like the aboveembodiment. The control unit controls On/Off of current supply withrespect to the coil winding body 221 so as to produce a one-way magneticfield in the conductor member 260, and produces a force so that theconductor member 260 can move in a refrigerant suction direction, i.e.,a bottom dead center direction unlike the above embodiment. Here,preferably, only the rear main springs S2 are installed between thesupporter 310 and the rear cover 320 to grant a restoration forceagainst a force applied to the movable member 130 by the linear motor200. Moreover, preferably, the elastic modulus and number of the rearmain springs S2 are determined to be proportional to the coil windingnumber of the coil winding body 221 as in the above embodiment.Therefore, when the current is input to the coil winding body 221, amagnet flux forms a closed circuit along the first and second stators220 and 240 due to the current flowing through the coil winding body221. Since an induction field is produced in the conductor member 260due to the magnetic flux, the force is applied in a bottom dead centerdirection, so that the conductor member 260 and the movable member 130move in the bottom dead center direction to suck the refrigerant. Next,when the current is not input to the coil winding body 221, the magnetflux and the induction field are vanished, and the conductor member 260and the movable member 130 move in a top dead center direction due tothe restoration force of the rear main springs S2. Such a process isrepeated to suck, compress and discharge the refrigerant.

As illustrated in FIG. 5, a further embodiment of the first stator 220is constructed such that first and second coil winding bodies 221A and221B wound with a coil in a circumferential direction are positioned ata certain interval in an axial direction, and core blocks 222 aremounted on the first and second coil winding bodies 221A and 221B. Thecoil is wound around the first and second coil winding bodies 221A and221B in the same direction. The control unit performs a control tosupply currents having a phase difference of 90° to the first and secondcoil winding bodies 221A and 221B, respectively, to produce a two-waymagnetic field in the conductor member 260, and repeats a process ofproducing a force so that the conductor member 260 can move in arefrigerant compression direction, i.e., a top dead center direction,and producing a force so that the conductor member 260 can move in arefrigerant suction direction, i.e., a bottom dead center direction.

Here, preferably, the front main springs S1 are installed between themotor cover 300 and the supporter 310 and the rear main springs S2 areinstalled between the supporter 310 and the rear cover 320 to grant arestoration force against a force applied to the movable member 130 bythe linear motor 200. In addition, preferably, the elastic modulus andnumber of the front main springs S1 and the rear main springs S2 aredetermined to be proportional to the coil winding number of the firstand second coil winding bodies 221A and 221B.

Accordingly, when the current is input to the first coil winding body221A, as the currents having AC waveforms with a phase difference of 90°are input to the first and second coil winding bodies 221A and 221B, themagnetic flux also has AC waveforms. Since an induction field isproduced in the conductor member 260 due to the magnetic flux, the forceis applied alternately in top and bottom dead center directions, so thatthe conductor member 260 and the movable member 130 repeat a process ofmoving in the top dead center direction to compress the refrigerant andmoving in the bottom dead center direction to suck the refrigerant.

The construction and operation of the conductor member 260 applied tothe linear compressor so constructed will be described below in moredetail.

FIGS. 6 to 8 are perspective views illustrating various embodiments ofthe conductor member applied to the linear compressor according to thepresent invention.

As illustrated in FIG. 6, an embodiment of the conductor member 260 isformed of a conductor material such as Cu and Al in a shapecorresponding to a connection member 290, e.g., a cylindrical shape.Here, the conductor member 260 is mounted on one end of the connectionmember 290 by an adhesive or an adhesion member, and the connectionmember 290 is installed to connect the conductor member 260 to themovable member 130. Surely, the connection member 290 has the sameconstruction as the conventional one, and has various holes 291 inportions other than the mounting portion of the conductor member 260 toreduce a passage resistance or radiate heat.

As illustrated in FIG. 7, another embodiment of the conductor member 270is formed in a cylindrical shape by alternately stacking an annular ironpiece 270 a and a ring conductor 270 b. Like the above embodiment, theconductor member 270 is mounted on one end of a connection member 290 byan adhesive or an adhesion member, and the connection member 290 isinstalled to connect the conductor member 270 to the movable member 130.The ring conductor 270 b may be formed of a conductor material such asCu and Al.

As illustrated in FIG. 8. a further embodiment of the conductor member280 is formed by winding a conductor line. The conductor member 280 ismounted to be wound around the outside of one end of a connection member290 or the outside of the connection member 290, and the connectionmember 290 is installed to connect the conductor member 280 to themovable member 130.

The conductor members 260, 270 and 280 shown in FIGS. 6 to 8 arepreferably formed of Al or Cu, and have the feature of beingmagnetically induced by an electromagnetic force. Since the conductormembers 260, 270 and 280 are applied to the linear motor 200, thepresent invention can more reduce manufacturing expenses than the priorart using the magnet.

FIG. 9 is a graph showing magnetic flux waveforms of the linear motorshown in FIG. 5 by an applied current. When the control unit appliespower to the linear motor 200 including the first and second coilwinding bodies 221A and 221B, with respect to currents flowing throughthe first stator 220, a current I_(M) of the first coil winding body221A and a current I_(A) of the second coil winding body 221B have ACwaveforms with a phase difference of 90°. Therefore, a syntheticmagnetic field B_(S) of the first stator 220 by the current shows ACwaveforms. The produced magnetic field linearly reciprocates, alternatedin positive and negative directions like the waveforms of the currentsI_(M) and I_(A).

FIG. 10 is a schematic circuit view for applying a current to the linearmotor shown in FIG. 5. For example, when an AC current is applied to aterminal I-I′, the current I_(A) applied to the second coil winding body221A is the AC current applied through a capacitor C, and has a phasedifference of 90° from the current I_(M) applied to the first coilwinding body 221A.

FIG. 11 is a graph showing linear reciprocation magnetic flux operationsof the linear motor shown in FIG. 5. FIG. 11 provides a graph showingthe current I_(M) of the first coil winding body 221A, the current I_(A)of the second coil winding body 221B, and the synthetic magnetic fieldB_(S) of the first stator 220 in the application of the current, and atable showing the linear reciprocation magnetic flux operations of thelinear motor 200 in points a to f existing in one period. That is, thetable of FIG. 11 shows that the first and second coil winding bodies221A and 221B are repeatedly magnetized into N-S and S-N poles in thepoints a to f according to the applied voltage.

More specifically, in the points a, b and c, B_(S) which is the sum ofI_(M) and I_(A) appears in a positive direction, i.e., an N pole, and anamplitude thereof increases and then decreases, and in the points d, eand f, B_(S) which is the magnetic field sum of I_(M) and I_(A) appearsin a negative direction, i.e., an S pole, and an amplitude thereofincreases and then decreases. As noted above, the magnetic flux isalternated in the positive/negative directions by the first coil windingbody 221A and the second coil winding body 221B, and the electromagneticforce of the first and second stators 220 and 240 and the inductionfield of the conductor member 260 interwork with each other.

FIG. 12 is a graph showing the relation between a slip and a torque ofthe linear motor applied to the present invention.

In general, preferably, the linear compressor is designed to operate ina resonance state so as to improve efficiency. When a load increases, arefrigerant gas in the linear compressor is expanded, so that an elasticmodulus of a gas spring increases. A mechanical resonance frequency ofthe linear compressor also increases. In order to make the linearcompressor operate in the resonance state, preferably, an LC resonancefrequency (a resonance frequency by the first coil winding body 221Aand/or the second coil winding body 221B and/or the capacitor C notedabove) which is an electrical resonance frequency is varied to be equalto a mechanical resonance frequency varied according to the load.Therefore, the linear compressor employing the linear motor 200 adoptingthe conductor member 260 according to the present invention is designedso that the LC resonance frequency can be varied according to the loadto follow the mechanical resonance frequency. That is, when the loadincreases, e.g. when an ambient temperature rises from a low to hightemperature, since a speed of the movable member 130 in a hightemperature state is slower than that in a low temperature state due toincrease of the elastic modulus of the refrigerant gas, a coolingcapacity decreases. To compensate for such decrease, the LC resonancefrequency is made to be equal to the mechanical resonance frequency inthe high temperature state, so that mechanical efficiency can beimproved by resonance. Accordingly, while the LC resonance frequency isdesigned to be approximate to the mechanical resonance frequency in thehigh temperature state, it is designed to become automatically largerthan the mechanical resonance frequency in the low temperature state.Here, preferably, in the high temperature state, the linear compressoroperates in a state approximate to the resonance state rather than inthe resonance state so as to reduce noise. Therefore, when the linearcompressor wherein the LC resonance frequency is designed to be equal oralmost equal to the mechanical resonance frequency in a high load isapplied to e.g., a refrigerator, the linear motor 200 automaticallyregulates a freezing capacity, and the refrigerator naturally modulatesthe cooling capacity according to the load.

When the linear motor 200 adopting the conductor member 260 operates,the relation between the slip which is a speed of the movable member 130and the torque which is a force moving the movable member 130 will beexamined in more detail. As illustrated in FIG. 12, when the linearmotor 200 is initially driven, the slip and the torque rise to beproportional. When the linear motor 200 stably operates in a slip ofover a certain value or a set value, the slip and the torque areinversely proportional regardless of a load. Here, an S-T curve becomesdifferent according to the load. A represents an S-T curve in a lowtemperature state, B represents an S-T curve in a high temperaturestate, and C represents an S-T curve produced considering variations ofthe mechanical resonance frequency.

That is, when the linear motor 200 operates in a state moving from a lowtemperature region II to a high temperature region I, the speed of themovable member 130 exists near a synchronous speed and falls. Althoughthe speed of the movable member 130 falls, since the LC resonancefrequency is approximate to the mechanical resonance frequency to ensurethe operation in the resonance state, mechanical efficiency ismaximized, so that the speed of the movable member 130 and the forcemoving the movable member 130 increase to thereby raise the stroke andmodulate the cooling capacity according to the load. Surely, since theLC resonance frequency is designed to be equal or approximate to themechanical resonance frequency in the high load, the movable member 130operates to reach a top dead center, and stably performs compression. Asthe operation is performed in the resonance state, efficiency of thecompressor is maximized.

On the contrary, when the linear motor 200 operates in a state movingfrom the high temperature region Ito the low temperature region II, thespeed of the movable member 130 exists near the synchronous speed.Although the speed of the movable member 130 rises, since the LCresonance frequency becomes much larger than the mechanical resonancefrequency to be distant from the resonance state, mechanical efficiencyis degraded, so that the speed of the movable member 130 and the forcemoving the movable member 130 decrease to thereby drop the stroke andmodulate the cooling capacity according to the load. The linearcompressor mechanically designed using the mechanical resonancefrequency varied according to the load adopts the current directapplication method, and does not require special controlling formodulating the cooling capacity according to the load. As a result, thelinear compressor does not require a special control apparatus andcontrol method, which simplifies the controlling. The linear compressorof this embodiment does not forcibly or artificially vary the amplitudeor frequency of power applied to the linear motor to modulate thecooling capacity, but naturally or automatically modulates the coolingcapacity. Surely, while naturally modulating the cooling capacity, thelinear compressor can forcibly modulate the cooling capacity.

The current direct application method, which is the mechanical designmethod using the mechanical resonance frequency varied according to theload, is nothing but an example of the control methods for naturallymodulating the cooling capacity according to the load. Besides, a directapplication method which is a mechanical design method optimizing therelation between a slip and a torque regardless of a load, an AC choppermethod and a triac phase control method which are methods using appliedvoltage variations, and an inverter method which is a method usingapplied frequency variations can also be used.

While the present invention has been described in connection with thepreferred embodiments, the present invention is not limited thereto andis defined by the appended claims. Therefore, it will be understood bythose skilled in the art that various modifications and changes can bemade thereto without departing from the spirit and scope of theinvention defined by the appended claims.

The invention claimed is:
 1. A linear compressor, comprising: a fixedmember provided with a compression space; a movable member whichlinearly reciprocates inside the fixed member to compress refrigerant;one or more springs installed to elastically support the movable memberin a motion direction; a first stator applied with a current to producea magnetic field; a second stator spaced apart from the first stator ata certain interval; a conductor member electromagnetically induced bythe magnetic field produced by the first stator and the second stator tomake the movable member linearly reciprocate; and a control unit whichcontrols supply of the current with respect to the first stator,wherein, when the movable member operates over a certain speed, a speedof the movable member and a force moving the movable member areinversely proportional at different ratios according to an amplitude ofa load.
 2. The linear compressor of claim 1, further comprising aconnection member which connects the movable member to the conductormember, wherein the conductor member is a conductor mounted on one endof the connection member.
 3. The linear compressor of claim 1, furthercomprising a connection member which connects the movable member to theconductor member, wherein the conductor member is formed by alternatelystacking an annular iron piece and a conductor, and mounted on one endof the connection member.
 4. The linear compressor of claim 1, furthercomprising a connection member which connects the movable member to theconductor member, wherein the conductor member is a conductor line woundaround one end of the connection member.
 5. The linear compressor ofclaim 1, wherein the first stator comprises a coil winding body woundwith a coil, and a core mounted on the coil winding body, and thecontrol unit controls On and Off of a current supply with respect to thecoil winding body so as to produce a one-way magnetic field in theconductor member.
 6. The linear compressor of claim 5, wherein thesprings comprise one or more of a first spring installed to elasticallysupport the movable member in a refrigerant compression direction, and asecond spring installed to elastically support the movable member in theopposite direction to the refrigerant compression direction.
 7. Thelinear compressor of claim 1, wherein at least some portion of theconductor member is positioned between the first stator and the secondstator.
 8. The linear compressor of claim 7, wherein the first statorcomprises first and second coil winding bodies spaced apart at aninterval in an axial direction and wound with a coil, respectively, anda core mounted on the first and second coil winding bodies, and thecontrol unit performs a control to supply currents having a phasedifference to the first and second coil winding bodies to produce atwo-way magnetic field in the conductor member.
 9. The linear compressorof claim 8, wherein the coil is wound around the first and second coilwinding bodies in the same direction, and a capacitor is connected inseries to one of the first and second coil winding bodies.
 10. Thelinear compressor of claim 8, wherein the control unit supplies currentshaving a phase difference of 90° to the first and second coil windingbodies.
 11. The linear compressor of claim 8, wherein the springs are afirst spring installed to elastically support the movable member in arefrigerant compression direction, and a second spring installed toelastically support the movable member in the opposite direction to therefrigerant compression direction.
 12. The linear compressor of claim 1,wherein, the control unit varies the amplitude or frequency of powerapplied to the first stator.
 13. The linear compressor of claim 1,wherein, if the movable member operates below a certain speed, when theload increases, the speed of the movable member increases, and the forcemoving the movable member increases.
 14. The linear compressor of claim13, wherein the control unit controls supply of the current toautomatically vary a stroke according to the load.
 15. The linearcompressor of claim 1, wherein, when the load increases, an electricalresonance frequency becomes approximate to a mechanical resonancefrequency.
 16. A linear compressor, comprising: a fixed member providedwith a compression space; a movable member which is provided with aconductor member, and linearly reciprocates inside the fixed member tocompress refrigerant; a plurality of springs installed to elasticallysupport the movable member in a motion direction; a first stator appliedwith a current to magnetically induce the conductor member; a secondstator positioned corresponding to the first stator so that at leastsome portion of the conductor member can be positioned in a spacebetween the first stator and the second stator; and a control unit whichcontrols supply and interception of power with respect to the firststator, wherein, when a load increases, an electrical resonancefrequency becomes approximate to a mechanical resonance frequency, sothat the linear compressor performs an automatic cooling capacitymodulation control, wherein, when the movable member operates over acertain speed, a speed of the movable member and a force moving themovable member are inversely proportional at different ratios accordingto the amplitude of the load.
 17. The linear compressor of claim 16,wherein the control unit varies the amplitude or frequency of powerapplied to the first stator to selectively perform a forcible coolingcapacity modulation control.